In highly-automated driving, monitoring the setpoint trajectory computed by the vehicle before it is traveled is indispensable for reasons of safety. Fundamentally, the setpoint trajectory including all detected objects is checked for collisions. If a setpoint trajectory is to result in a collision, it is classified as inadvisable and is not traveled. However, it is generally not trivial to determine the actual size (in particular width and length) of objects. In particular surroundings sensors, for example, a radar sensor or a monocamera, are at best capable of recognizing that an object is located somewhere in the field of vision. This sensor typically may not determine the precise contour of the object. Therefore, checking trajectories based on detected objects is not always expedient.